Why do people grow hair under their nose? Why does it grow down instead of up?
–Riley, 11, Prior Lake, MN

Humans have hair all over their bodies, including above the upper lip. Of course, not all hair is quite the same. A lot of people have very fine hairs on their faces. Others can sprout a thick beard or mustache.

Cats don’t have mustaches, but we do have whiskers. In fact, hair is one of the things mammals have in common. Even dolphins have it. Hair can help keep us warm and protected from the elements.

Human hairs sprout from tiny little sacks in the skin called follicles. The root of the hair grows out of a follicle and feeds off tiny blood vessels to keep growing. Some hair follicles are too small for the eye to see. As males develop from kids to adults, the size of the follicles can get bigger.

This change is related to a chemical in the body called testosterone, said my friend Lori Nelson, a biologist at Washington State University. When follicles get bigger, the hair also gets thicker, and it can draw some attention to the upper lip.

Many males have facial hair because they have more testosterone circulating in their blood than females do. But having more testosterone doesn’t always mean you’ll have more hair, Nelson adds.

She said there’s been some debate over whether or not facial hair might also help with attracting a mate. I suppose the exact purpose of a mustache is still a bit of a mystery. It’s an interesting observation you make about the direction the hairs grow, too.

At first, I thought the answer would be right under my nose. My guess was that it had something to do with gravity pulling the hair toward the ground. But it turns out the trajectory of your hair follicles is actually determined when you are still growing inside your mother’s womb.

That’s what I found out from my friend Ryan Driskell, a researcher at WSU who studies wounds and how the skin regenerates.

He explained how some of your cells use different chemicals to communicate with one another. The messages they carry can include instructions for how to form different parts of a human body.

Some of these chemicals will even direct hair to grow in a specific direction, Driskell said. These particular chemicals tell follicles on the upper lip to point downward. Each hair that sprouts out points downward, too.

Driskell isn’t just interested in why hair grows, but also why it sometimes doesn’t grow back. While we have medical procedures that help repair wounds, hair follicles and sweat glands are often damaged. They don’t regenerate. Driskell’s research is helping us learn how to help the human and other animal bodies heal even better.

Sincerely,
Dr. Universe

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